Dynamic link adaption for time division duplex (TDD)

ABSTRACT

A UE system implements dynamic link adaptation by adding or changing control information to notify a receiver which timeslots and codes are currently active and which timeslots should be avoided. The UE provides synchronization such that the receiver knows which timeslots and codes the UE has used to map the coded composite transport channel onto physical channels. The UE attempts to avoid the timeslots which are experiencing transmission difficulties, while attempting to utilize the timeslots which are not experiencing transmission problems.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/311,710 filed Aug. 10, 2001.

BACKGROUND

The present invention relates to the field of wireless communications.More particularly, the present invention relates to a time divisionduplex (TDD) communication system which uses dynamic link adaptation fortransmissions between user equipment (UE) and a base station (BS) toadjust for changing propagation conditions.

Third generation (3G) cellular systems are able to transmit a wide rangeof services, from high data rate services such as video and Internetdownloads, to low data rate services such as speech. Referring to FIG.1, a plurality of user services are shown as individual data streams.These individual data streams are assigned to transport channels A, B,C, whereby the data streams are coded and multiplexed. Each transportchannel A, B, C is assigned a specific coding rate and a specifictransmission time interval (TTI). The coding rate determines the numberof transmitted bits of the physical layer, and the TTI defines thedelivery period of the block of data to be transmitted. For example, theTTI may be either 10, 20, 40 or 80 ms.

Multiple transport channels A, B, C are multiplexed together into acoded composite transport channel (CCTrCh). Since the CCTrCh is made upof a plurality of transport channels A, B, C, it may have a plurality ofdifferent coding rates and different TTIs.

For example, transport channel A may have a 20 ms TTI and transportchannel B may have a 40 ms TTI. Accordingly, the formatting of transportchannel A in the first 20 ms and the formatting of transport channel Ain the second 20 ms can change. In contrast, since transport channel Bhas a 40 ms TTI, the formatting, and hence the number of bits, are thesame for each 20 ms period over the 40 ms TTI duration. It is importantto note that all of the transport channels A, B, C are mapped to theCCTrCh on a TTI basis, using the smallest TTI within the CCTrCh. Thetransmit power is ultimately determined based on transport formatcombination applied in the smallest TTI within the CCTrCh.

It should be noted by those of skill in the art that each individualdata stream will have an associated data rate, and each physical channelwill have an associated data rate. Although these data rates are relatedto each other, they are distinctly different data rates.

Once the smallest TTI within the CCTrCh has been established, it must bedetermined how many bits of data will be transmitted and which transportchannels will be supported within a given TTI. This is determined by theformatting of the data.

A transport format combination (TFC) is applied to each CCTrCh based onthe smallest TTI. This essentially specifies for each transport channelhow much data is transmitted in a given TTI and which transport channelswill coexist in the TTI.

A TFC set is the set of all of the possible TFCs. If the propagationconditions do not permit all of the possible TFCs within the TFC set tobe supported by the UE, a reduced set of TFCs which are supported by theUE is created. This reduced set is called a TFC subset. TFC selection isthe process used to determine which data and how much data for eachtransport channel A, B, C to map to the CCTrCh. A transport formatcombination indicator (TFCI) is an indicator of a particular TFC, and istransmitted to the receiver to inform the receiver which transportchannels are active for the current frame. The receiver, based on thereception of the TFCIs, will be able to interpret which physicalchannels and which timeslots have been used. Accordingly, the TFCI isthe vehicle which provides coordination between the transmitter and thereceiver such that the receiver knows which physical transport channelshave been used.

In TDD, the UE typically calculates the required transmit power basedupon a signal to interference ratio (SIR) target that it receives fromthe base station. Knowing the TFC selected, the UE calculates therequired transmission power. If the RF propagation conditions areoptimal, a TFC will be selected such that the maximum number of bits aretransmitted in each timeslot. However, as RF propagation conditionsdeteriorate and the UE calculates a required power that is higher thanthe maximum allowable power of the UE in order to transmit all of thedesired information, a different set of TFCs, (i.e., the aforementionedTFC subset), must be selected which will be supportable by the maximumallowable power of the UE. This ultimately reduces the amount of datathat the physical layer has to support, and reduces the powerrequirement.

In summary, the system chooses on a TTI basis which transport channelswill be active and how much data will be transmitted in each one. TheTFC selection process takes into account the physical transmissiondifficulties, (maximum allowable power being one), and reduces thephysical transmission requirements for some time duration.

After the multiple transport channels A, B, C are combined into a singleCCTrCh, the CCTrCh is then segmented and those segments are mappedseparately onto a number of physical channels. In TDD systems, thephysical channels may exist in one, or a plurality of differenttimeslots, and may utilize a plurality of different codes in eachtimeslot. Although there are as many as 16 possible codes in a timeslotin the downlink, it is more typical to have, for example, 8 codes in aparticular downlink in a particular timeslot. In the uplink, there israrely more than two codes in a particular timeslot. In any event, thereare a number of physical channels defined by a plurality of codes in aplurality of timeslots. The number of physical channels can vary.

In the Universal Mobile Telecommunications System (UTMS) time divisionduplex (TDD) mode, the CCTrCh is mapped onto the physical channels byassigning the timeslots and the codes in consecutive order. For example,the first timeslot is selected for mapping. The first code of the firsttimeslot is assigned first, and then the remaining codes of the firsttimeslot are each assigned consecutively until the last code has beenassigned. Once all of the codes from the first timeslot are assigned,the second timeslot is entered. The mapping process is repeated usingeach of the codes from the second timeslot consecutively until they haveall been assigned.

The mapping process for a specific user equipment (UE) under UMTS isshown in the example of FIG. 2A having 12 timeslots (S1–S12), 8 codes ineach timeslot (0–7), and 12 total codes (A_(1–A) ₁₂) to beallocated/configured. Those codes and timeslots that are shown as“shaded” are considered, for purposes of illustration, not to beallocatable to the present UE, (since they may have been allocated toother UEs). The allocatable portions of timeslots S4–S7 will be assignedin consecutive order starting at timeslot S4, and codes 0–4 in eachtimeslot will be also assigned in consecutive order. Assuming that 12codes will be mapped in this manner, the result is a mapping shown inFIG. 2A with code A₁ being assigned first and code A₁₂ being assignedlast.

Although the prior art process shown in FIG. 2A provides one option formapping the data from the CCTrCh onto the physical channels, there aresome drawbacks with this process when transmission problems areencountered within a single timeslot, for example, when the desiredtransmission power exceeds the maximum allowable UE power. The processof consecutive assignment of timeslots and codes for mapping the CCTrChonto the physical channels as set forth in the UMTS-TDD standard tendsto exaggerate the problems when a transmission problem occurs. By way ofillustration, due to the consecutive manner in which timeslots areallocated/configured when a transmission problem occurs, it typicallyoccurs in one or several of the earlier timeslots. When the systemdetects a problem, for example, when the desired transmission powerexceeds the maximum allowable UE power for a certain TTI, the systemselects new TFCs such that the data requirements on all of the timeslotsare reduced. Since the UMTS-TDD standard specifies that timeslots areassigned consecutively, if the transmission problem is in one of thefirst several timeslots, the system will still begin packing data intothe earlier timeslots, where the problem is at its worst, and will leavethe last timeslots relatively empty, where there are no transmissionproblems.

As a result, the system exacerbates the problem since data raterequirements are lowered on the timeslots where there is not a problem,and timeslots that have a problem will still be packed with data. Thisis an inefficient utilization of the radio resources.

SUMMARY

The present invention is a TTD UE which implements dynamic linkadaptation by adding or changing control information to notify thereceiver which timeslots and codes are currently active and whichtimeslots should be avoided. Thus, the UE provides synchronization suchthat the receiver knows which timeslots and codes the UE has used to mapthe CCTrCh onto physical channels. The UE attempts to avoid thetimeslots which are experiencing transmission difficulties, whileattempting to utilize the timeslots which are not experiencingtransmission problems.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a block diagram of individual data streams being combined intoa physical channel.

FIG. 2A is the result of a prior art code mapping process.

FIG. 2B is a prior art data burst.

FIG. 3A is a data burst structure of the first embodiment having acontrol field located in data field 1.

FIG. 3B is a data burst structure of the first embodiment having acontrol field located in data field 2.

FIG. 3C is a data burst structure of the first embodiment having acontrol field located in the midamble.

FIG. 3D is a data burst structure of the first embodiment having acontrol field located in both data fields.

FIG. 3E is an example allocation/configuration of timeslots in the firstembodiment.

FIG. 4A is a data burst structure of the second embodiment having thefirst TFCI field modified.

FIG. 4B is a data burst structure of the second embodiment having thesecond TFCI field modified.

FIG. 4C is a data burst structure of the second embodiment having bothTFCI fields modified.

FIG. 4D is an example allocation/configuration of timeslots in thesecond embodiment.

FIG. 5A is a data burst structure of the third embodiment having anencoded bit pattern in data field 1.

FIG. 5B is a data burst structure of the third embodiment having anencoded bit pattern in data field 2.

FIG. 5C is a data burst structure of the third embodiment having anencoded bit pattern in the midamble.

FIG. 5D is a data burst structure of the third embodiment without TFCIfields, having an encoded bit pattern in data field 1.

FIG. 5E is a data burst structure of the third embodiment without TFCIfields, having an encoded bit pattern in data field 2.

FIG. 5F is a data burst structure of the third embodiment without TFCIfields, having an encoded bit pattern in the midamble.

FIG. 5G is an example allocation/configuration of timeslots in the thirdembodiment.

FIG. 6A is a data burst structure of the fourth embodiment having aninterference information field located in data field 1.

FIG. 6B is a data burst structure of the fourth embodiment having aninterference information field located in data field 2.

FIG. 6C is a data burst structure of the fourth embodiment having aninterference information field located in the midamble.

FIG. 6D is an example allocation/configuration of timeslots in thefourth embodiment.

FIG. 7A is the data burst structure of the fifth embodiment.

FIG. 7B is an example allocation/configuration of timeslots in the fifthembodiment.

FIG. 8A is the data burst structure of the sixth embodiment.

FIG. 8B is an example allocation/configuration of timeslots in the sixthembodiment.

FIG. 8C is an example allocation/configuration of timeslots in analternative to the fifth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention will be described with reference to the drawingsfigures wherein like numerals represent like elements throughout.

Referring to FIG. 2B, a prior art data burst is shown. The data burstcomprises two data fields separated by a midamble which are followed bya guard period (GP). The TFCI is transmitted within one or both of thedata fields of the burst. The number of coded TFCI bits depends upon thenumber of possible TFCs that are supported. Since the TFCI istransmitted within the data fields, each bit required to transmit theTFCI reduces the number of user data bits. Therefore, it is desirable tolimit the number of TFCI bits.

The location of the TFCI adjacent to the midamble allows for the bestpossible transmission, since interference from the midamble can becanceled and the channel estimate is most reliable for bits adjacent tothe midamble. As those of skill in the art should realize, the datafields comprise both user data and physical control fields, althoughthese fields will not be described in further detail hereinafter.

The present invention comprises six different embodiments for performingdynamic link adaptation. The first embodiment, as shown in FIGS. 3A–3E,comprises adding a new control field to the data burst to indicate whichparticular timeslots are active, and which timeslots should be avoided.For example, as shown in FIG. 3A, a control field has been added to datafield 1. FIG. 3B shows the control field added to data field 2.Alternatively, FIG. 3C shows the control field as part of the midamble.FIG. 3D shows the control field added to both data field 1 and datafield 2. Although the control field(s) are shown in a particularlocation within the data fields, they may be located in any portion ofthe data field.

In any of the alternatives shown in FIG. 3A–3D, it is important to notethat the control field identifies the timeslots to which the receivershould look for valid data. The data in the control field may refer to“active” timeslots which include valid data; may include “inactive”timeslots which have invalid data and are to be avoided (hereinafter“inactive” timeslots); or may include both active and inactivetimeslots. The active or inactive timeslots may be identifiedindividually, or the identifier may include a bit string, with a oneindicating an active timeslot and a zero indicating an inactivetimeslot. It also should be noted that the control field can comprise aseparately delineated control field or may simply reside in a portion ofthe data fields.

Referring to FIG. 3E, the allocation/configuration of timeslots usingthe method of the first embodiment is shown. In this example, it isassumed that the control fields shown in FIGS. 3A–3D indicate thattimeslots S4, S6 and S7 are active, and that S5 is inactive.Accordingly, timeslot S5 is not used, and codes A1–A12 areallocated/configured in timeslots S4, S6 and S7. This permits the systemto avoid an “offending” timeslot, such as timeslot S5 in this example,which will not adequately support a communication without a substantialincrease in UE power output.

Referring to FIGS. 4A–D, a second embodiment of the present invention isshown. In this embodiment, one or both of the TFCI fields are expandedand/or modified to include the extra data regarding which timeslots areactive and which are inactive. FIG. 4A shows the first TFCI fieldexpanded and/or modified in order to include the extra data; FIG. 4Bshows the second TFCI field expanded and/or modified in such a way; andFIG. 4C shows both TFCI fields expanded and/or modified in such a way.

Referring to FIG. 4D, the allocation/configuration of the timeslotsusing the method of the second embodiment is shown. In this example, itis assumed that the control fields shown in FIGS. 4A–4C indicate thattimeslot S6 is inactive and timeslots S4, S5 and S7 are active.Accordingly, the codes are assigned/configured such that timeslot S6 isavoided and timeslots S4, S5 and S7 are assigned/configured with thecodes in consecutive order. Timeslot S4 will be filled first, followedby timeslots S5 and S7 consecutively.

Referring to FIGS. 5A–5F, a third embodiment is shown. In thisembodiment, a special encoded bit pattern is added to one or both of thedata fields or the midamble within the data burst; for example datafield 1 as shown in FIG. 5A, data field 2 as shown in FIG. 5B or themidamble as shown in FIG. 5C. By including this special encoded bitpattern within a data burst, the transmitter indicates that these areinactive timeslots, which are to be avoided. When the receiver detectsthe special encoded bit pattern in the data burst, the informationassociated with that timeslot is discarded or otherwise ignored.

FIGS. 5D–5F are similar to FIGS. 5A–5C except that the data burst doesnot include the TFCI fields. As shown in FIG. 5D, the encoded bitpattern may be included at any location within data field 1.Alternatively, as shown in FIG. 5E, the encoded bit pattern may belocated within data field 2, or as shown in FIG. 5F may be locatedwithin the midamble. Although the encoded bit pattern located withindata field 1 or data field 2 is preferably located close to themidamble, this is not required in the present embodiment or any of theother embodiments. Additionally, the encoded bit pattern may be minimal,as shown in FIGS. 5A–5D and 5F, or may comprise most or all of the datafield as shown in FIG. 5E.

The length of the bit pattern is such that a high gain coding scheme maybe used so that it can be received with reduced power. Thus, forexample, if a 256 chip sequence is used, then the power requirements arereduced relative to a spreading factor of 16, by 12 dB. In onealternative, a sync-like (Golay) sequence that does not require channelestimation may be used.

FIG. 5G shows an allocation/configuration of timeslots using the methodof the third embodiment. In this example, it is assumed that the databursts shown in FIGS. 5F have indicated that timeslot S6 has beendesignated as inactive. Thus, the data burst associated with timeslot S6will include the special encoded bit pattern. As a result, timeslots S4,S5 and S7 will be allocated/configured consecutively and timeslot S6will be avoided.

The fourth embodiment of the present invention ranks all activetimeslots in order of decreasing interference, and then the channelallocation/configuration is made based upon the interference levels.

Preferably, the transmitter periodically performs interferencemeasurements in each timeslot for the amount of interference and sendsthis information to the receiver. Once the timeslots are ranked basedupon the interference level, the timeslots with the least interferenceare filled first and the timeslots with the worst interference arefilled last. The interference information, or rank, may be transmittedfrom the transmitter to the receiver in one of the fields of the databurst, or a new field may be created; for example data field 1 as shownin FIG. 6A, data field 2 as shown in FIG. 6B or the midamble as shown inFIG. 6C.

The measurements used for ranking the timeslots are those which are wellknown to those of skill in the art, such as the channel quality CQmeasurements that are signaled between the RNC, the RNS and the Node Bin a 3G system. The node B may also use higher layer signaling with anacknowledgement to prioritize the channel allocation/configuration.

FIG. 6D illustrates an allocation/configuration of timeslots using themethod of the fourth embodiment. In this example, it is assumed thattimeslot S6 has the least amount of interference, timeslot S5 has thesecond least amount of interference, timeslot S7 has the third leastamount and timeslot S4 has the most interference. Accordingly, thetimeslots will be filled in the following order: S6, S5, S7 and S4, asshown in FIG. 6D.

The fifth embodiment in accordance with the present invention creates aneven distribution of data across all timeslots. In this embodiment,referring to FIG. 7A, a TFC is chosen, and the corresponding TFCIs aretransmitted in the TFCI fields, that reduce the data rate evenly acrossall timeslots to the point where the offending timeslot can support thedata transmission. This embodiment is the most simple solution since theTFCIs that are transmitted are the same as in the prior art. However,the system allocates/configures timeslots and codes such that the datais evenly distributed across all of the timeslots.

The method of the fifth embodiment results in anallocation/configuration of timeslots shown in FIG. 7B. As shown, thecodes are allocated such that the data is distributed evenly across alltimeslots. This embodiment has the additional advantages that no newfields are needed and no synchronization between the transmitter andreceiver has to be performed in order to make a notification of activeor inactive timeslots since all timeslots are active.

In a sixth embodiment in accordance with the present invention shown inFIG. 8A, the inactive timeslot, and all timeslots thereafter, are notused to send any information. The TFCI is used to convey which timeslotsshould be used. However, when the UE calculates maximum allowable powerwill be exceeded in a certain timeslot, such as timeslot S5, thattimeslot and all subsequent timeslots are not used.

The result of the sixth embodiment is a code allocation/configurationshown in FIG. 8B. In this example, it is assumed that timeslot S5 is theinactive timeslot. Accordingly, since the offending timeslots and alltimeslots thereafter are discarded, only timeslot S4 will be used andonly codes A1–A5 will be allocated/configured.

In an alternative to the embodiment, the inactive timeslot may still beused, albeit in a lesser capacity. As shown in FIG. 8C, less codes maybe assigned to that timeslot to reduce the burden on the timeslot.

A summary of the different embodiments of the present invention is shownin Table 1 below.

TABLE 1 EMBODIMENT FIGS. First 3A–3E Add a new control field to one orboth data fields, or to the midamble, to indicate active and/or inactivetimeslots Second 4A–4D Modify one or both TFCI fields to indicate activeand/or inactive timeslots Third 5A–5G Add an encoded bit pattern to alltimeslots that are inactive Fourth 6A–6D Rank timeslots in order ofdecreasing interference; use the timeslots with the least interferencefirst Fifth 7A–7B Choose a TFC such that the “offending” timeslot cansupport a reduced data rate, and average resource allocations across alltimeslots Sixth 8A–8B Maximum power is determined for each specifictimeslot. Resource units are not applied to the timeslot that exceedsmaximum allowable power and all timeslots thereafter.

It should be noted that one drawback in implementing the presentinvention is the location of the TFCI and the control information foractive and inactive timeslots, (hereinafter “timeslot information”).Since the TFCI typically exists only in certain timeslots, it ispossible to have a communication that uses five timeslots, butdesignates only timeslot 2, or timeslots 1 and 4, to have the TFCIand/or the timeslot information. The TFCI and the timeslot informationare necessary to synchronize the transmitter and the receiver in theprocessing of the data. However, there may be instances when the onlytimeslots that have the TFCI or the timeslot information will be thetimeslots that exceed the maximum allowable transmission power.

For the first four embodiments of the present invention and describedwith reference to FIGS. 3A–6D, if the TFCI or the timeslot informationare in only the timeslots that have been designated as inactive, thecommunication will fail.

One solution to this problem is to put the TFCI and timeslot informationin at least two timeslots; and potentially every used timeslot when dataloss is a greater concern. This will ensure that if the receiverreceives a timeslot, it will also receive the TFCI and timeslotinformation.

For the fifth and sixth embodiments shown and described with referenceto FIGS. 7A–8B, the TFCI problem does not exist. For the fifthembodiment, the data rate is reduced, but all timeslots are still usedand the TFCI and timeslot information will always be available. Thesixth embodiment will always include the TFCI and timeslot informationin the first timeslot.

It should be noted that although the present invention has beendescribed with reference to the uplink, it is equally applicable to thedownlink; and utilizing the teachings of the embodiments as describedherein in both the uplink and the downlink are contemplated herein aswithin the scope of the present invention.

While the present invention has been described in terms of the preferredembodiment, other variations, which are within the scope of theinvention as outlined in the claims below will be apparent to thoseskilled in the art.

1. A User Equipment (UE) that supports a communication using a wirelesshybrid time division multiple access (TDMA)/code division multipleaccess (CDMA) format by selecting and utilizing at least one timeslotfrom a plurality of available timeslots and at least one code from aplurality of codes, the UE comprising: means for calculating, for eachavailable timeslot, the power required to transmit data; means fordetermining whether said calculated power for each timeslot exceeds athreshold; means for removing timeslots exceeding said threshold fromsaid available timeslots to determine remaining timeslots; means forsignaling an identifier of said remaining timeslots to anothercommunicating unit; and means for using said remaining timeslots and thecodes within said remaining timeslots to support the communication. 2.The UE of claim 1, wherein said signaling means further includes meansfor using a data burst comprising first and second data fields,separated by a midamble, followed by a guard period.
 3. The UE of claim2, wherein said identifier lists the remaining timeslots.
 4. The UE ofclaim 2, wherein said identifier lists the exceeding timeslots.
 5. TheUE of claim 2, wherein said identifier lists the remaining and exceedingtimeslots.
 6. The UE of claim 3, wherein said identifier is locatedwithin at least one of said data fields.
 7. The UE of claim 3, whereinsaid identifier is located within said midamble.
 8. The UE of claim 2,wherein said data burst further comprises two TFCI fields, locatedbefore and after said midamble.
 9. The UE of claim 8, wherein saididentifier is located with at least one of said TFCI fields.
 10. The UEof claim 1, wherein the codes are allocated consecutively.
 11. A UserEquipment (UE) which implements dynamic link adaption in a time divisionduplex (TDD) communication system by transmitting timeslot and codeallocation information in a data burst, the data burst having aplurality of fields including two data fields separated by a midamblefield, the UE comprising: means for transmitting, in at least one ofsaid fields, an indication of timeslots to be used; and means forallocating codes to said used timeslots in consecutive order until allcodes have been assigned.
 12. The UE of claim 11, wherein saidindication is transmitted within at least one of said data fields. 13.The UE of claim 11, wherein said indication is transmitted within saidmidamble field.
 14. The UE of claim 11, wherein said data burst furtherincludes first and second TFCI fields, said first TFCI field locatedbefore said midamble field and said second TFCI field located after saidmidamble field, whereby said indication is transmitted within at leastone of said TFCI fields.
 15. A User Equipment (UE) which signals codeand timeslot assignments to support a communication of a user in awireless hybrid time division multiple access (TDMA)/code divisionmultiple access (CDMA) communication system, utilizing at least onetimeslot from a plurality of available timeslots and at least one codefrom a plurality of codes, the UE comprising: means for calculating, foreach available timeslot, the power required to transmit data; means fordetermining whether said calculated power for each timeslot exceeds apredetermined threshold; means for loading information to support saiduser communication in a first set of timeslots that do not exceed saidpredetermined threshold; means for loading an encoded bit pattern in asecond set of timeslots that exceed said predetermined threshold; meansfor signaling said first and second sets of timeslots to anothercommunicating unit; and means for using said information from said firstset of timeslots to support the communication.
 16. The UE of claim 15,wherein said loading means uses consecutive codes from said plurality ofcodes.
 17. A User Equipment (UE) which signals code and timeslotassignments in a time division duplex communication format, the UEcommunicates with at least a second unit, utilizing at least onetimeslot from a plurality of available timeslots and at least one codefor each timeslot from a plurality of codes for each timeslot, the UEcomprising: means for calculating the power required to transmit datafor each available timeslot; means for determining whether saidcalculated power exceeds a threshold; means for removing timeslotsexceeding said threshold from said available timeslots to determineremaining timeslots; means for signaling an identifier of said remainingtimeslots; and means for using said remaining timeslots to support thecommunication.
 18. The UE of claim 17, wherein at least one codecomprises a plurality of codes, and wherein said using means uses codesin consecutive order.
 19. A User Equipment (UE) which implements dynamiclink adaption in a time division duplex communication system bytransmitting timeslot and code allocation information in a data burst,the data burst having a plurality of fields including two data fieldsseparated by a midamble field, the UE comprising: means for determininginactive timeslots and active timeslots; means for transmitting, in atleast one of said fields, an indication of active timeslots; means forconsecutively allocating codes to active timeslots until all codes havebeen allocated.